Thrust film cartridges utilizing film door light traps have been used in the photographic industry as an alternative to conventional film cartridges utilizing plush light traps. Typical thrust film cartridges include an outer shell having a longitudinally-extending opening for allowing for the exit of film from the cartridge. A cartridge spool is rotatably positioned within the outer shell to accommodate a roll of film. A film door is rotatably mounted adjacent the opening and is movable between a closed position, wherein a light tight seal is formed, and an open position, wherein film is allowed to exit the cartridge.
Thrust film cartridges are particularly useful for allowing rewinding and subsequent reloading of film before the complete roll of film is used. Cameras having the ability to rewind and reload partially-used rolls of film are sometimes referred to as mid-roll interrupt ("MRI") cameras. Such a camera is disclosed in commonly-assigned U.S. Pat. Nos. 4,947,197 to Smart et al. and 4,965,600 to Smart et al., which are incorporated in their entirety herein by reference.
In order to prevent opening of the film door when the camera door is open, some cameras provide mechanisms for ensuring that the camera door is securely closed before the film door may be opened. In addition, such cameras attempt to ensure that the film door is securely closed before the camera door may be opened. It is further desirable to provide a mechanism wherein the film door cannot be forced closed when film is extending from the thrust film cartridge.
Commonly-assigned U.S. Pat. No. 5,231,438 to Smart, the specification of which is incorporated in its entirety herein by reference, discloses such an apparatus wherein a latch for securing the camera door locked and closed is also responsible for opening and closing the film door of a thrust film cartridge. Specifically, the latch is forced into the locked position by the action of a slide plate, and the slide plate is forced into the locked position by the action of a plate spring. A slide button is utilized to force the slide plate into the unlocked position, and a separate button spring is provided for biasing the slide button into the locked position. A latch spring forces the latch from the locked to the unlocked position. The latch spring has a spring force which is high enough to rotate the latch and thereby open the film door and camera door under normal operating conditions, but which is not high enough to force the film door closed if film is extending from the cartridge. Accordingly, if film is extending from the cartridge, the latch will not move completely to the open position and, therefore, will not allow the camera door to be opened. As is evident from the above description, the camera disclosed in Smart utilizes six elements to provide the above-noted features.
With the popularity of inexpensive, manually-wound cameras, it is typically desirable to design new camera mechanisms to be simple and inexpensive. Accordingly, it can be appreciated that it would be desirable to provide a simple, inexpensive mechanism for ensuring that the camera door is securely closed whenever the film door of a thrust film cartridge is open, and for ensuring that the film door is securely closed before the camera door may be opened. In addition, it would be desirable if the film door cannot be forced closed, and therefore the camera door cannot be opened, when film is extending from the thrust film cartridge.